The Shadow Chancellor struggled to recall the rate of National Insurance on
live television in his latest gaffe about the economy.

Alan Johnson has been dogged by claims that he is not knowledgeable enough to be an effective opponent to George Osborne in times of economic hardship.

His latest slip was seized upon by both Conservatives and the Liberal Democrats as an example of his lightweight ability.

Mr Johnson appeared on Sky News on Sunday to criticise the Coalition Government’s announcement that VAT will rise to 20 per cent, a move he described as “fiscal fundamentalism”.

Labour wants to increase national insurance as a way of tackling the deficit.

Accused of being an economic “novice”, Mr Johnson said: “The accusation of economic novice is that when you take over a new job, you have to ensure that you bone up on these things.”

A few seconds later, presenter Dermot Murnaghan asked the shadow minister to give the current rate of employers’ national insurance contributions.

Mr Johnson tried to avoid the question before he said it would increase by one per cent, rising from 20 per cent to 21 per cent.

Mr Murnaghan interrupted, to say: “Sorry, National Insurance, employers' secondary class one-rate for employers, stands at the moment at …?”

There was an awkward pause where Mr Johnson appeared unable to answer before the presenter came to his rescue, telling him the figure of 12.8 per cent.

Mr Murnaghan went on: “Right, OK, I helped you out there. Just out of interest, there is still a lot to learn for you in terms of the job.”

The shadow chancellor replied: “There's not a lot to learn about how we tackle this deficit.”

His apparent lack of basic knowledge was described as “utterly incredible” by Stephen Williams, co-chairman of the Liberal Democrat Treasury Backbench Committee.

“Britain is facing the highest debt levels in peacetime history, yet we have a Labour party that's completely clueless on basic economics,” he said.

“Jobs will not be created by the fantasy economics conjured up on Alan Johnson's abacus.

“Continuing to advocate a jobs tax when he appears not to understand its basic facts smacks of economic illiteracy and incompetence.”

Mr Williams said that the former Education Secretary was supposed to be an asset for Labour leader Ed Miliband, but was “fast becoming an embarrassment”.

He went on: "Labour left the country in an economic shambles. They have made no apology, they have no regrets and with a self-proclaimed novice at their economic helm, it's little wonder they still offer no alternative."

Tory MP Matthew Hancock, who was chief of staff to George Osborne before the General Election, said: "Labour's threadbare credibility took another dive today as Alan Johnson admitted he didn't know the level of National Insurance, the very tax he wants to put up.

“Every time Labour speak on the economy they show they have no credibility, no ideas, and no plan to deal with the historic mess they did so much to create.”

Mr Johnson’s appointment to Shadow Chancellor last October came as a surprise after Labour stalwarts Ed Balls or his wife Yvette Cooper were seen as the favourites.

In December, Mr Johnson admitted that he too had been surprised by the appointment and added that he would be willing to give up his brief if David Miliband wanted to return to front line politics.

In recent months, he has been criticised for mistakes, including suggesting that the VAT rise would affect food bills, when food largely remains unaffected by VAT.

He also raised eyebrows when he claimed that Labour would aim to clear the budget deficit by 2015, before saying he “probably” meant 2016.

:: Unfortunate gaffes:

– September 24, 2010: Before being appointed shadow chancellor, he talked about the Coalition’s policies: “Imagine knocking on the doors on the Gipsyville estate saying yeah, your child trust fund's gone and your child benefit's frozen and your jobs have gone and you're paying more for your food because of the hike in VAT.”

VAT actually rarely affects food.

– October 9, 2010: When asked what his first move would be as shadow chancellor, he said: “Pick up a primer – 'economics for beginners’.”

– December 4, 2010: Mr Johnson said he would be willing to give way to David Miliband if he wished to return to front line politics: “I’d be delighted if David served in the shadow cabinet, and I have no better person to keep the seat warm for.”

– January 4, 2011: On the Today programme, when asked what Labour would do to tackle the budget deficit, he replied: “We set out £57 billion of savings in something called the Budget which is itemised in the Red Book.

“And you’ll know it very well, you’ve probably read more of it than I have."

– January 4, 2011: On the same programme, when asked if the deficit was as bad as the Coalition was suggesting, he said: “No, we need to get the structural deficit eradicated. We plan to do that by about 2015-16.”

A few hours later, he told journalists that he “probably meant 2016-2017”.